U.S. patent number 11,314,100 [Application Number 16/252,484] was granted by the patent office on 2022-04-26 for forming a homogenized illumination line which can be imaged as a low-speckle line.
This patent grant is currently assigned to Cognex Corporation. The grantee listed for this patent is Cognex Corporation. Invention is credited to Laurent Belanger, John F. Filhaber, Andrew Goodale, Andrew Parrett, Ronald Zimmerman.
United States Patent |
11,314,100 |
Parrett , et al. |
April 26, 2022 |
Forming a homogenized illumination line which can be imaged as a
low-speckle line
Abstract
A system for forming a homogenized illumination line which can
be imaged as a low-speckle line is disclosed. The system includes a
laser configured to emit a collimated laser beam; and an
illumination-fan generator that includes one or more linear
diffusers. The illumination-fan generator is arranged and
configured to (i) receive the collimated laser beam, (ii) output a
planar fan of diffused light, such that the planar fan emanates
from a light line formed on the distal-most one of the one or more
linear diffusers, and (iii) cause formation of an illumination line
at an intersection of the planar fan and an object.
Inventors: |
Parrett; Andrew (Boston,
MA), Filhaber; John F. (East Haddam, CT), Goodale;
Andrew (Maynard, MA), Belanger; Laurent (Hudson, NH),
Zimmerman; Ronald (Boulder, CO) |
Applicant: |
Name |
City |
State |
Country |
Type |
Cognex Corporation |
Natick |
MA |
US |
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Assignee: |
Cognex Corporation (Natick,
MA)
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Family
ID: |
1000006262000 |
Appl.
No.: |
16/252,484 |
Filed: |
January 18, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190227336 A1 |
Jul 25, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62619675 |
Jan 19, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01B
11/25 (20130101); G02B 5/0278 (20130101); G02B
27/48 (20130101); G01N 21/8901 (20130101); G01N
21/956 (20130101); G01N 21/8806 (20130101); G02B
5/0215 (20130101); G01N 2021/8908 (20130101) |
Current International
Class: |
G02B
27/48 (20060101); G01N 21/88 (20060101); G01N
21/89 (20060101); G02B 5/02 (20060101); G01N
21/956 (20060101); G01B 11/25 (20060101) |
Field of
Search: |
;353/30 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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Jun 2014 |
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103869474 |
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Jun 2014 |
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CN |
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104965307 |
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Oct 2015 |
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CN |
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105210112 |
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Dec 2015 |
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CN |
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105474090 |
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Apr 2016 |
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CN |
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102016211339 |
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Dec 2016 |
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DE |
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WO2009077198 |
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Jun 2009 |
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WO |
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WO2012032668 |
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Mar 2012 |
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WO |
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Other References
Chinese Patent Application No. 201910049286.5, First Office Action
dated Jul. 28, 2020, with translation (17 pages). cited by
applicant .
Optotune Switzerland AG, "Compact and Reliable Speckle Reduction",
Aug. 2017, 41 pages. cited by applicant .
Sales et al., RPC Photonics, Inc., "Deterministic microlens
diffuser for Lambertian scatter", presented at the SPIE 2006 Annual
Meeting, San Diego, California, Aug. 30, 2006, 19 pages. cited by
applicant .
German Patent Application No. 10 2019 000 272.5, Examination Report
dated Feb. 4, 2021 with machine translation, 7 pages. cited by
applicant .
Korean Patent Application No. 10-2019-0007556, Notice of
Preliminary Rejection and Translation, dated May 26, 2020, 9 pages.
cited by applicant .
Japanese Patent Application No. 2019-007821, Notice of Reason(s)
for Refusal, dated Mar. 17, 2020, 8 pages. cited by
applicant.
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Primary Examiner: Brooks; Jerry L
Attorney, Agent or Firm: Fish & Richardson P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority under 35 U.S.C.
.sctn. 119(e)(1) of U.S. Provisional Application No. 62/619,675,
filed on Jan. 19, 2018, which is incorporated by reference herein.
Claims
What is claimed is:
1. A system comprising a laser configured to emit a collimated
laser beam; an illumination-fan generator that comprises a
fan-shaped beam generator and a linear diffuser, wherein the
illumination-fan generator is arranged and configured to receive
the collimated laser beam, output a planar fan of diffused light,
such that the planar fan of diffused light emanates from a light
line formed on the linear diffuser, and cause formation of an
illumination line at an intersection of the planar fan of diffused
light and an object; and an image acquisition device disposed such
that its optical axis forms an acute angle to the planar fan of
diffused light, and configured to form an image of the illumination
line, wherein the image comprises an average of a sequence of
images of instances of the illumination line formed during an
exposure time interval.
2. The system of claim 1, wherein the fan-shaped beam generator is
arranged and configured to receive the collimated laser beam and
form a fan-shaped beam that intersects the linear diffuser along
the light line parallel to a direction of diffusion of the linear
diffuser, and wherein the linear diffuser transmits light
corresponding to the light line to form the planar fan.
3. The system of claim 1, wherein the fan-shaped beam generator
comprises a linear diffuser.
4. The system of claim 1, wherein the linear diffuser comprises one
of a pseudorandom cylinder array or a holographic optical
element.
5. The system of claim 1, wherein the fan-shaped beam generator
comprises one of a cylindrical lens or a Powell lens.
6. The system of claim 1, wherein a divergence angle of a
fan-shaped beam formed by the fan-shaped beam generator is larger
than a target divergence angle, and a separation (d) between the
fan-shaped beam generator and the linear diffuser is larger than a
predetermined separation to ensure that a length (L.sub.X) of the
light line formed by the fan-shaped beam on the linear diffuser is
larger than a target length, the predetermined separation being
proportional to the target divergence angle and the target
length.
7. The system of claim 1, comprising a driver configured to cause
cyclical motion of the linear diffuser relative to the fan-shaped
beam generator, the cyclical motion being along a direction of
diffusion of the linear diffuser.
8. The system of claim 7, wherein the driver is configured to
deactivate the laser when a speed of the cyclical motion is below a
predetermined speed, and the predetermined speed is inversely
proportional to the exposure interval.
9. The system of claim 1, wherein the image acquisition device is
configured to form an image of the illumination line as a
homogenized line.
10. A system comprising: a laser configured to emit a collimated
laser beam; and an illumination-fan generator that comprises at
least one linear diffuser having a direction of diffusion, wherein
the illumination-fan generator is arranged and configured to
receive the collimated laser beam, output a planar fan of diffused
light, such that the planar fan of diffused light emanates from a
light line formed on a distal-most of the at least one linear
diffuser, and cause formation of an illumination line at an
intersection of the planar fan of diffused light and an object; and
wherein the at least one linear diffuser comprises a
cylindrical-shell shaped linear diffuser arranged with its axis
perpendicular to a direction of propagation of the collimated laser
beam, and configured to receive the collimated laser beam at an
input portion of the cylindrical-shell shaped linear diffuser, form
a fan-shaped beam that intersects an exit portion of the
cylindrical-shell shaped linear diffuser along the light line
parallel to the direction of diffusion, and transmit through the
exit portion light corresponding to the light line to form the
planar fan.
11. The system of claim 10, wherein the at least one linear
diffuser comprises one of a pseudorandom cylinder array or a
holographic optical element.
12. The system of claim 10, wherein a divergence angle of a
fan-shaped beam formed by an input portion of the cylindrical-shell
shaped linear diffuser is larger than a target divergence angle,
and a diameter of the cylindrical-shell shaped linear diffuser is
larger than a predetermined diameter to ensure that a length
(L.sub.X) of a diffused-light contour formed by the fan-shaped beam
on the exit portion of the cylindrical-shell shaped linear diffuser
is larger than a target length, the predetermined diameter being
proportional to the target divergence angle and the target
length.
13. The system of claim 10, comprising a driver configured to cause
rotation of the cylindrical-shell shaped linear diffuser about its
axis, the rotation being along a direction of diffusion of the
cylindrical-shell shaped linear diffuser.
14. The system of claim 13, comprising an image acquisition device
disposed such that its optical axis forms an acute angle to the
planar fan of diffused light, and configured to form an image of an
illumination line as a de-speckled image, wherein the de-speckled
image comprises an average of a sequence of images of instances of
the illumination line formed during an exposure time interval.
15. The system of claim 10, comprising an image acquisition device
disposed such that its optical axis forms an acute angle to a
planar fan of diffused light, and configured to form an image of
the illumination line as a homogenized line.
16. The system of claim 1, wherein the linear diffuser has random
differences in surface roughness at different locations of a scan
path.
17. The system of claim 16, wherein the linear diffuser comprises
one of a pseudorandom cylinder array or a holographic optical
element.
18. The system of claim 16, comprising a driver configured to cause
cyclical motion of the linear diffuser relative to the fan-shaped
beam generator, the cyclical motion being along a direction of
diffusion of the linear diffuser.
Description
FIELD OF THE DISCLOSURE
Technologies are described for producing a planar sheet of laser
light for illuminating an object, such that the illumination line
formed at the intersection of the planar sheet with the object is
homogenized and can be imaged as a de-speckled line.
BACKGROUND
Laser light is projected, in a sheet or fan, from a light source to
an object where its intersection forms an illumination line. The
illumination line is imaged, in many applications using a camera,
to determine a level of a surface of the object relative a
reference surface, or a profile of the object. The fidelity of an
image of the illumination line is impacted negatively by sparkle or
speckle. Sparkle is caused by spurious reflections of the laser
light off a facetted surface of the object. Speckle is caused by
the interference of coherent laser light with differing phase
caused by reflections of the coherent light off an optically-rough
surface of the object. These effects create an uneven and locally
distorted image of the illumination line at (i) the camera
acquiring the image of the illumination line, or (ii) viewer
viewing the illumination line. As such, these effects can reduce
the accuracy of laser light-based measurements of an object.
SUMMARY
Technologies described herein use a fan-shaped beam generator and a
linear diffuser disposed between the light source and the object,
such that each of the fan-shaped beam generator and the linear
diffuser spreads, along a predetermined direction, light
transmitted there through. The fan-shaped beam generator can itself
be a linear diffuser, or can be one of a Powell lens or a
cylindrical lens. Additionally, the fan-shaped beam generator and
the linear diffuser can be moved relative to each other along the
predetermined direction. In either of these cases, laser light
transmitted through the fan-shaped beam generator and the linear
diffuser is projected in a sheet or fan to an object where its
intersection with the sheet or fan forms an illumination line that
(i) is homogenized along the predetermined direction and (ii) has a
Gaussian profile (or another profile associated with the laser
light emitted by the source) perpendicular to the predetermined
direction, regardless of variations in the height of the object
over the span of the illumination line. In the case when the
fan-shaped beam generator and the linear diffuser are moving
relative to each other, the homogenized illumination line formed at
the intersection of the sheet or fan with the object can be imaged
(and/or observed) as a de-speckled line.
According to an aspect of the disclosed technologies, a system
includes a laser configured to emit a collimated laser beam; and an
illumination-fan generator that includes one or more linear
diffusers. The illumination-fan generator is arranged and
configured to (i) receive the collimated laser beam, (ii) output a
planar fan of diffused light, such that the planar fan emanates
from a light line formed on the distal-most one of the one or more
linear diffusers, and (iii) cause formation of an illumination line
at an intersection of the planar fan and an object.
The foregoing and other embodiments can each optionally include one
or more of the following features, alone or in combination. In some
implementations, the linear diffuser comprises one of a
pseudorandom cylinder array or a holographic optical element.
In some implementations, the illumination-fan generator can include
a fan-shaped beam generator, and a linear diffuser having a
direction of diffusion. Here, the fan-shaped beam generator is
arranged and configured to receive the collimated laser beam and
form a fan-shaped beam that intersects the linear diffuser along
the light line parallel to the direction of diffusion.
Additionally, the linear diffuser transmits light corresponding to
the light line to form the planar fan. In some cases, the
fan-shaped beam generator can include a linear diffuser. In cases,
the fan-shaped beam generator can include one of a cylindrical lens
or a Powell lens. In some implementations, a divergence angle of a
fan-shaped beam formed by the fan-shaped beam generator is larger
than a target divergence angle. Additionally, a separation "d"
between the fan-shaped beam generator and linear diffuser is larger
than a predetermined separation to ensure that a length of a light
line formed by the fan-shaped beam on the linear diffuser is larger
than a target length "L.sub.X". Here, the predetermined separation
is proportional to the target divergence angle and the target
length.
In some implementations, the system can include a driver configured
to cause cyclical motion of the linear diffuser relative to the
fan-shaped beam generator. Here, the cyclical motion is along a
direction of diffusion of the linear diffuser. Further, the system
can include an image acquisition device disposed such that its
optical axis forms an acute angle to the planar fan of diffused
light, and configured to form an image of the illumination line as
a de-speckled image. Here, the de-speckled image includes an
average of a sequence of images of instances of the illumination
line formed during an exposure time interval. Furthermore, the
driver is configured to deactivate the laser when a speed of the
cyclical motion is below a predetermined speed, and the
predetermined speed is inversely proportional to the exposure
interval.
In some implementations, the illumination-fan generator can include
a cylindrical-shell shaped linear diffuser arranged with its axis
perpendicular to a direction of propagation of the collimated laser
beam, and configured to (i) receive the collimated laser beam at an
input portion of the cylindrical-shell shaped linear diffuser, (ii)
form a fan-shaped beam that intersects an exit portion of the
cylindrical-shell shaped linear diffuser along the light line
parallel to the direction of diffusion, and (iii) transmit through
the exit portion light corresponding to the light line to form the
planar fan. In some implementations, a divergence angle of a
fan-shaped beam formed by an input portion of the cylindrical-shell
shaped linear diffuser is larger than a target divergence angle.
Additionally, a diameter of the cylindrical-shell shaped linear
diffuser is larger than a predetermined diameter to ensure that a
length of a diffused-light contour formed by the fan-shaped beam on
the exit portion of the cylindrical-shell shaped linear diffuser is
larger than a target length "L.sub.X". Here, the predetermined
diameter is proportional to the target divergence angle and the
target length.
In some implementations, the system can include a driver configured
to cause rotation of the cylindrical-shell shaped linear diffuser
about its axis, the rotation being along a direction of diffusion
of the cylindrical-shell shaped linear diffuser. Further, the
system can include an image acquisition device disposed such that
its optical axis forms an acute angle to the planar fan of diffused
light, and configured to form an image of an illumination line as a
de-speckled image. Here, the de-speckled image includes an average
of a sequence of images of instances of the illumination line
formed during an exposure time interval.
In some implementations, the system can include an image
acquisition device disposed such that its optical axis forms an
acute angle to a planar fan of diffused light, and configured to
form an image of the illumination line as a homogenized line.
Particular aspects of the disclosed technologies can be implemented
to realize one or more of the following potential advantages. For
example, in accordance with the disclosed technologies, the quality
of the illumination line along the line and perpendicular to the
line is better than what can be achieved using only a Powell lens
without using the companion linear diffuser, as disclosed, because
unwanted diffractive and refractive effects caused by the Powell
lens can be transferred in the image of the illumination line. As
another example, the fan of light produced in accordance with the
disclosed technologies can be effectively Gaussian in the direction
perpendicular to the fan plane, while in the fan plane, the
illumination profile can be designed to satisfy various
illumination profiles. As yet another example, the disclosed
technologies effectively reduce the coherence of the laser light
without impacting the quality of the illumination line in the
direction perpendicular to the line direction. As yet another
example, by using a fan-shaped beam generator followed by a linear
diffuser, the power of a laser included in the light source can be
increased without laser safety concerns due to the eye now viewing
an extended (potentially high intensity) light source.
Details of one or more implementations of the disclosed
technologies are set forth in the accompanying drawings and the
description below. Other features, aspects, descriptions and
potential advantages will become apparent from the description, the
drawings and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1B show aspects of an example of a laser-based imager that
forms a homogenized illumination line.
FIGS. 2A-2C show aspects of an example of a laser-based imager that
forms a homogenized illumination line, which can be imaged as a
low-speckle line.
FIG. 3 shows another example of a laser-based imager that forms a
homogenized illumination line, which can be imaged as a low-speckle
line.
FIGS. 4A-4C show aspects of a linear diffuser that can be part of
the laser-based imagers of FIGS. 1A, 2A and 3.
Certain illustrative aspects of the disclosed technologies are
described herein in connection with the following description and
the accompanying figures. These aspects are, however, indicative of
but a few of the various ways in which the principles of the
disclosed technologies may be employed and the disclosed
technologies are intended to include all such aspects and their
equivalents. Other advantages and novel features of the disclosed
technologies may become apparent from the following detailed
description when considered in conjunction with the figures.
DETAILED DESCRIPTION
FIG. 1A shows an example of a laser-based imager 100 that uses a
homogenized illumination line 137. The imager 100 includes a
laser-based illumination-fan source 102 and an image acquisition
device 140. The source 102 has an optical axis 101, here (for
example) oriented along the z-axis, and is configured to output,
along the optical axis and parallel to the (x,z) plane, a planar
fan of diffused light 135. The planar fan 135 is projected onto an
object 190 and forms the illumination line 137 at the intersection
of the planar fan with the object. Note that the illumination line
137 follows a contour of the object 190, regardless of whether the
object has a curved or flat surface.
The source 102 includes a laser 110 and an illumination-fan
generator 120. The laser 110 is arranged and configured to emit
laser light as a collimated laser beam 111 along the optical axis
101. A wavelength of the laser light emitted by the laser 110 can
be in the range of 400-2000 nm. The illumination-fan generator 120
is arranged and configured to receive the collimated laser beam 111
and to produce the planar fan of diffused light 135.
The illumination-fan generator 120 includes a fan-shaped beam
generator 122 having an optical axis common to the optical axis
101, and one or more linear diffusers having a direction of
diffusion perpendicular to the optical axis 101, here (for example)
along the x-axis. The fan-shaped beam generator 122 and the one or
more linear diffusers are distributed along the optical axis 101.
The fan-shaped beam generator 122 is arranged and configured to
spread the collimated laser beam 111 along the x-axis as a
fan-shaped beam 123. In the example shown in FIG. 1A, the
illumination-fan generator 120 includes a single linear diffuser
132 that has a direction of diffusion that is perpendicular to the
optical axis 101, here (for example) along the x-axis. Note that
the fan-shaped beam generator 122 can itself be a linear diffuser
that has a direction of diffusion along the x-axis, or can be one
of a Powell lens or a cylindrical lens. In the latter case, each of
the Powell lens or the cylindrical lens has optical power in the
(y-z) plane and lacks optical power in the (x,z) plane. The
fan-shaped beam generator 122 is supported by a first mount 124 and
the linear diffuser 132 is supported by a second mount 134 spaced
apart from the first mount, such that the fan-shaped beam generator
122 is disposed between the laser 110 and the linear diffuser
132.
The laser 110 projects the laser beam 111 onto the fan-shaped beam
generator 122 as a beam spot 113. The fan-shaped beam generator 122
transmits light corresponding to the beam spot 113 to form a
fan-shaped beam 123 parallel to the (x,z) plane. Note that when the
fan-shaped beam generator 122 is implemented as a liner diffuser,
the fan-shaped beam 123 is formed from transmitted light that is
diffused along the x-axis (and not diffused along the y-axis). When
the fan-shaped beam generator 122 is implemented as a Powell lens
or a cylindrical lens, the fan-shaped beam 123 is formed from
transmitted light that is redirected along the x-axis (and not
redirected along the y-axis). As such, the fan-shaped beam
generator 122 projects the fan-shaped beam 123 onto the linear
diffuser 132 as a light line 127 along the x-axis. Note that when
the fan-shaped beam generator 122 is implemented as a linear
diffuser, the fan-shaped beam 123 of diffused light is projected on
the linear diffuser 132 as a diffused light line 127. The linear
diffuser 132 transmits light corresponding to the light line 127 to
form the planar fan of diffused light 135 parallel to the (x,z)
plane. Note that that planar fan 135 is a superposition of
fan-shaped beams 133 (which are parallel to the (x,z) plane), each
of the fan-shaped beams being formed by the linear diffuser 132 by
diffusing light radiated from a corresponding point of the light
line 127. As such, the linear diffuser 132 projects the planar fan
of diffused light 135 onto the object 190 as the homogenized
illumination line 137.
In some implementations, the linear diffuser 132 can be one of a
linear diffusing random cylinder array (e.g., random in radius,
numerical aperture (NA), and depth), pseudo-random engineered
cylinder array, or holographic optical element, each of which are
configured to provide the fan-shaped beams of diffused light 133
when light corresponding to points of the light line 127 transmits
there through. Each fan-shaped beam 133 has a diffusion angle, here
in the (x,z) plane, determined by the characteristics of the
cylinder array, e.g., values of radius, NA, and depth, for
instance. The fan-shaped beam generator 122, when implemented as a
linear diffuser, can be configured in the same manner as the linear
diffuser 132, or in a similar manner. Note that the fine structure
and pseudo-random nature of the linear diffuser 132, and of the
fan-shaped beam generator 122, when implemented as a linear
diffuser, provides enhanced uniformity, along the x-axis, of the
illumination line 137. At the same time, the profile along the
y-axis of the illumination line 137 (as well of the diffused-light
line 127) remains essentially the same as the profile along the
y-axis of the beam spot 113.
The disclosed linear diffuser 132, and in some implementations the
linear diffuser used as the fan-shaped beam generator 122, can be
implemented as an engineered diffuser, of appropriate parameters,
from among the EDL (engineered diffuser line) series manufactured
by RPC Photonics, Inc. of Rochester, N.Y. For example, FIG. 4A is a
side view in the (x-z) plane of a linear diffuser 422 from the EDL
series. Here, the linear diffuser surface varies along the x-axis
(here, oriented in the left-right direction), but is constant along
the y-axis (here, oriented in-out of the page.) FIG. 4B shows that
the measured light intensity of the fan-shaped beam formed by
EDL-40 has a top-hat angular profile 472. Here, the light intensity
of the fan-shaped beam is substantially constant over an angular
range of [-20.degree.,+20.degree. ] relative the (y-z) plane, and
drops abruptly (to substantially zero) for larger angles. More
specifically, for an input beam spot having a diameter of 5 mm, and
for a detector angle of 0.25.degree., the full-width at 90% (50%)
is 39.9.degree. (42.9.degree.). FIG. 4B also shows that the scatter
by the linear diffuser EDL-40 is relatively uniform within the
fan-shaped beam. Other models allow a smaller divergence of the
fan-shaped beam (e.g., down to +/-2.degree., for a total divergence
of 4.degree. for EDL-4) or greater divergence of the fan-shaped
beam (e.g., up to +/-60.degree., for a total divergence of
120.degree. for EDL-120). FIG. 4C is an image of a fan-shaped beam
profile 474 which shows that, for the linear diffusers from the EDL
series, the diffusion occurs exclusively along one direction (here
along the x-axis) and virtually no diffusion occurs in the
transverse direction (here along the y-axis). This ensures no
thickening/broadening of the planar fan of diffused light 135 and
thus of the illumination line 137.
Referring again to FIG. 1A, the image acquisition device 140 (e.g.,
a camera coupled with, or integrated into a common device housing
with, the laser-based illumination-fan source 102) is arranged and
configured to image the object 190 as illuminated with the
homogenized illumination line 137. Here, an optical axis 142 of the
image acquisition device 140 is arranged in the (y,z) plane and
forms an acute angle SA (i.e., larger than 0 and less than
90.degree.) with the optical axis 101 of the laser-based
illumination-fan source 102. The image acquisition device 140
includes an image sensor and an optical subsystem that forms an
image of the illumination line 137 on the image sensor. In some
implementations, the planar fan of diffused light 135, a plane of
the image sensor of the image acquisition device 140, and the acute
angle SA satisfy the Scheimpflug condition. The image sensor of the
image acquisition device 140 is configured to convert the image of
the illumination line 137 into information for producing a digital
image of the line-illuminated object 190.
Referring now to FIG. 1B, the illumination-fan generator 120
outputs the planar fan of diffused light 135 during operation of
the laser-based illumination-fan source. When an observer looks
straight into the generator 120, e.g., the observer's eye 142 being
placed on, or in the vicinity of, the optical axis 101, the planar
fan 135 intersects the eye along the contour 139. Under these
circumstances, the observer sees the light line 127 on the linear
diffuser 132, so the observer's eye 142 forms, on the retina 144,
an image 145 of the light line. If the line image 145 extends over
a length l.sub.X long enough for the light intensity (.varies.light
power/length) imparted to the retina to not exceed a safety
threshold, then the observer will not experience discomfort or
damage. Here, the safety threshold corresponds to a high level of
laser safety. Moreover, to ensure that the light intensity on the
retina 145 is below the noted safety threshold, a length L.sub.X of
the light line 127 on the linear diffuser 132 must exceed a
particular target for a given input light intensity at the beam
spot 113. To maximize the C6 safety correction factor in accordance
with laser safety standards set forth by the International
Electrotechnical Commission (IEC), the length L.sub.X must be at
least 10 mm and the diffusion angle must be at least 6.degree.. As
such, the length L.sub.X can be 10, 30, 50 or 100 mm. The length
L.sub.X of the light line 127 can be controlled by (i) the
separation d along the z-axis between the fan-shaped beam generator
122 and the linear diffuser 132, and (ii) the divergence angle of
the fan-shaped beam 123. For example, for a given divergence angle,
the length L.sub.X increases/decreases when the separation d
increases/decreases. As another example, for a given separation d,
the length L.sub.X increases/decreases when the divergence angle
increases/decreases. Note that in FIG. 1B, the distance D between
the observer's eye 142 and the linear diffuser 132, and the
separation d between the fan-shaped beam generator 122 and the
linear diffuser 132 are not drawn to scale, as the ratio Did can be
as large as 10.
Note that, for an illumination-fan generator having only a
fan-shaped beam generator, e.g., the fan-shaped beam generator 122,
if the observer were looking straight into the illumination-fan
generator, then the observer would see the beam spot 113 on the
fan-shaped beam generator 122. As such, the observer's eye 142
would form, on the retina 144, an image of the beam spot 113. For
the same given input light intensity at the beam spot 113 discussed
above in connection with the illumination-fan generator 120, the
light intensity imparted to the retina by the image of the beam
spot would most likely exceed the noted safety threshold. As such,
the illumination-fan generator 120 can also satisfy a high level of
laser safety satisfied by conventional illumination-fan generators,
however the disclosed illumination-fan generator uses higher power
lasers than the conventional illumination-fan generators. A typical
laser profiling device or other machine vision device on the
market, which is limited to laser class 3R per the IEC 60825 laser
safety standards, is limited to providing a 5 mW-laser beam through
a 7 mm aperture positioned 100 mm away from the apparent source, to
protect eye safety. In accordance with the foregoing laser safety
standards, a C6 correction factor can be applied if the apparent
source cannot be imaged to a point on the eye. This factor is
determined by the included angle of the source, and how they eye
can image it. Assuming the beam is Gaussian and of negligible
thickness in the axis transverse to the fan, and that the extended
source (i.e., light line 127) is 10 mm long, the C6 would provide,
for the laser-based illumination-fan source 102, a corrective
factor of .about.30 to the AEL (acceptable exposure limit). As
such, the laser 110 of the laser-based illumination-fan source 102
could be configured to provide as much as 150 mW-laser beam
(30.times.5) through a 7 mm aperture positioned 100 mm away from
the apparent source and still protect eye safety.
Note that although homogenous, an illumination contour 137--formed
at an intersection of a planar fan 135, which is output by the
laser-based illumination-fan source 102, with an object 190--will
still present speckle when imaged by the image acquisition device
140 or observed by an observer under an acute angle (e.g., SA).
Improvements described below are capable of reducing the noted
speckle.
FIG. 2A shows an example of a laser-based imager 200 that uses a
homogenized illumination line 237 which can be imaged (and/or
observed) as a low-speckle line. The imager 200 includes a
laser-based illumination-fan source 202 and an image acquisition
device 240. In some implementations, the image acquisition device
240 can be the image acquisition device 140 described above in
connection with FIG. 1A. The source 202 has an optical axis 201,
here (for example) oriented along the z-axis, and is configured to
output, along the optical axis and parallel to the (x,z) plane, a
planar fan of diffused light 235. The planar fan 235 is projected
onto an object 290 and forms the illumination line 237 at the
intersection of the planar fan 235 with the object 290.
The source 202 includes a laser 210 and an illumination-fan
generator 220. In some implementations, the laser 210 can be the
laser 110 described above in connection with FIG. 1A. The laser 210
is arranged to emit laser light as a collimated laser beam 211
along the optical axis 201. The illumination-fan generator 220 is
arranged and configured to receive the collimated laser beam 211
and to produce the planar fan of diffused light 235.
The illumination-fan generator 220 includes a fan-shaped beam
generator 222 having an optical axis common to the optical axis
201, and one or more linear diffusers having a direction of
diffusion perpendicular to the optical axis 201, here (for example)
along the x-axis. The fan-shaped beam generator 222 and the one or
more linear diffusers are distributed along the optical axis 201.
The fan-shaped beam generator 222 is arranged and configured to
spread the collimated laser beam 211 along the x-axis as a
fan-shaped beam 223. In the example shown in FIG. 2A, the
illumination-fan generator 220 includes a single linear diffuser
232 that has a direction of diffusion that is also along the x-axis
and is spaced apart along the z-axis from the fan-shaped beam
generator 222, such that the fan-shaped beam generator 222 is
disposed between the laser 210 and the linear diffuser 232. In some
implementations, the fan-shaped beam generator 222 and the linear
diffuser 232 can be the respective fan-shaped beam generator 122
and the linear diffuser 132 described above in connection with FIG.
1A.
In the example shown in FIG. 2A, during operation of the source
202, at least one of the fan-shaped beam generator 222 and the
linear diffuser 232 will be cyclically moved along the direction of
diffusion, here (for example) along the x-axis. As such, the
fan-shaped beam generator 222 is supported by a first linear stage
224, and the linear diffuser 232 is supported by a second linear
stage 234. In some implementations, the first and second linear
stages 224, 234 can include one or more of guides, motors, voice
coils, piezos, etc. The first linear stage 224 is arranged along
the direction of beam expansion, and includes first linear
actuators 252 configured to cause the first linear stage to
cyclically move the fan-shaped beam generator 222 in the direction
of beam expansion. The second linear stage 234 is arranged along
the direction of diffusion, and includes second linear actuators
254 configured to cause the second linear stage to cyclically move
the linear diffuser 232 in the direction of diffusion.
In the example shown in FIG. 2A, the source 202 also includes a
driver 250 coupled with the laser 210 and with either the first
linear actuator 252, or the second linear actuator 254, or with
both. In other implementations, the driver 250 is external to the
source 202 and is coupled with the laser 210 and the first and
second linear actuators 252, 254. In this manner, the driver 250
can send control signals to the laser 210 and to the first and
second linear actuators 252, 254.
Referring now to operation of the source 202, the laser 210
projects the laser beam 211 onto the fan-shaped beam generator 222
as a beam spot 213. The fan-shaped beam generator 222 transmits
light corresponding to the beam spot 213 to form a fan-shaped beam
223 parallel to the (x,z) plane. As such, the fan-shaped beam
generator 222 projects the fan-shaped beam 223 onto the linear
diffuser 232 as a light line 227 along the x-axis. The linear
diffuser 232 transmits light corresponding to the light line 227 to
form the planar fan of diffused light 235 parallel to the (x,z)
plane. Note that that planar fan 235 is a superposition of
fan-shaped beams 233 (which are parallel to the (x,z) plane), each
of the fan-shaped beams 233 being formed by the linear diffuser 232
by diffusing light radiated from a corresponding point of the light
line 227. As such, the linear diffuser 232 projects the planar fan
of diffused light 235 onto the object 290 as the illumination line
237.
In some implementations, the fan-shaped beam generator 222 is
stationary relative the optical axis 201, and the linear diffuser
232 moves cyclically along the x-axis relative the optical axis 201
(e.g., the driver 250 deactivates the first linear actuators 252
and activates the second linear actuators 254). In these cases, the
fan-shaped beam generator 222 can be implemented either as (i) a
linear diffuser or (ii) one of a Powell lens or a cylindrical lens.
Here, the stationary light line 227 will be formed at multiple
locations of the moving linear diffuser 232, each location with its
own local roughness profile. FIG. 2B shows that when the linear
diffuser 232 is moved along the x-axis, the stationary light line
227 will be formed over a first scan path 231 of length P.sub.X,
which can be 2, 3, 5 or 10 times larger than the length L.sub.X of
the stationary light line, such that a local roughness at a
"location" of the first scan path is randomly different from local
roughness at any other locations of the first scan path. Here, a
location of the first scan path 231 has the length L.sub.X of the
light line 227. In this manner, multiple instances of the planar
fan 235 formed by the moving linear diffuser 232 will be randomly
different from each other, so multiple instances of the stationary
illumination line 237 formed on the stationary object 290 will also
be randomly different from each other. Randomly different speckle
patterns corresponding to the multiple instances of the stationary
illumination line 237 will average out over an exposure time of the
image acquisition device 240, so the stationary illumination line
237 will be imaged by the image acquisition device as a low-speckle
line. Note that in this case, the randomness of the speckle
patterns corresponding to the multiple instances of the stationary
illumination line 237 is caused, at least in part, by the random
differences of the surface roughness of the linear diffuser 232 at
the different locations of the first scan path 231.
In some implementations, the fan-shaped beam generator 222 moves
cyclically along the x-axis relative the optical axis 201, and the
linear diffuser 232 is stationary relative the optical axis 201
(e.g., the driver 250 activates the first linear actuators 252 and
deactivates the second linear actuators 254). In these cases, the
fan-shaped beam generator 222 is implemented as a linear diffuser,
and it is referred to as the first linear diffuser 222. In the same
context, the linear diffuser 232 is referred to as the second
linear diffuser 232. Here, the stationary beam spot 213 will be
formed at multiple points of the moving first linear diffuser 222,
each point with its own local roughness profile. FIG. 2C shows that
when the first linear diffuser 222 is moved along the x-axis, the
stationary beam spot 213 will be formed over a second scan path 221
of length P.sub.X, which can be 10, 20, 30, 50 or 100 times larger
than the diameter of the beam spot, such that a local roughness at
a "point" of the second scan path is randomly different from local
roughness at any other points of the second scan path. Here, a
point of the second scan path 221 has the size of the beam spot
213. In this manner, multiple instances of the fan-shaped beam of
diffused light 223 formed by the moving fan-shaped beam generator
222 will be randomly different from each other, so multiple
instances of the stationary diffused-light line 227 formed on the
stationary second linear diffuser 232 will also be randomly
different from each other. As such, multiple instances of the
planar fan 235 formed by the stationary second linear diffuser 232
will be randomly different from each other, so multiple instances
of the stationary illumination line 237 formed on the object 290
will also be randomly different from each other. Randomly different
speckle patterns corresponding to the multiple instances of the
stationary illumination line 237 will average out over an exposure
time of the image acquisition device 240, so the stationary
illumination line 237 will be imaged by the image acquisition
device as a low-speckle line. Note that in this case, the
randomness of the speckle patterns corresponding to the multiple
instances of the stationary illumination line 237 is caused, at
least in part, by the random differences of the surface roughness
of the first linear diffuser 222 at the different points of the
first scan path 221.
In some cases of the latter implementations, both the first linear
diffuser 222 and the second linear diffuser 232 move cyclically
along the x-axis relative the optical axis 201 (e.g., the driver
250 activates both the first linear actuators 252 and the second
linear actuators 254). Here, a phase of the relative motion between
the first and second linear diffusers 222, 232 is controlled by the
driver 250 to be different from zero, such that the two linear
diffusers are in motion relative to each other. In this case, the
randomness of the speckle patterns corresponding to the multiple
instances of the stationary illumination line 237 is caused, at
least in part, by a combination of (i) the random differences of
the surface roughness of the first linear diffuser 222 at the
different points of the second scan path 221, and (ii) the random
differences of the surface roughness of the second linear diffuser
232 at the different locations of the first scan path 231.
Referring again to FIG. 2A, to ensure that the illumination line
237 can be imaged as a low-speckle line, the driver 250 causes the
first linear stage 224 to hold the fan-shaped beam generator 222
stationary relative the optical axis 201, and the second linear
stage 234 to cyclically move the linear diffuser 232, relative to
the optical axis 201 and along the x-axis, with a predetermined
frequency. When the fan-shaped beam generator 222 is implemented as
a first linear diffuser 222, to ensure that the illumination line
237 can be imaged as a low-speckle line, the driver 250 causes the
first linear stage 224, or the second linear stage 234, or both to
cyclically move the first linear diffuser 222 and the second linear
diffuser 232, relative to each other and along the x-axis, with a
predetermined frequency. In either of these cases, the
predetermined frequency of the relative motion can be in the range
of 0.5-500 Hz. A particular value of the relative motion frequency
f can be chosen based on the required exposure time .DELTA.t
coupled with the range of travel .DELTA.X (e.g., along the first
scan path 231 or second scan path 221) required to reduce speckle
contrast C. The types of structured linear diffusers used, e.g., in
the illumination-fan generator 220 have features of size on the
order of 10-50 .mu.m. To achieve a .DELTA.t=5 ms (200 Hz) exposure
with a C=10% speckle contrast, the image acquisition device 240
averages
##EQU00001## independently random speckle patterns in 5 ms, or
20000 per second. With the speckle pattern changing roughly every
micron traveled along the first scan path 231 and/or the second
scan path 221, i.e., .delta.x=1 .mu.m. Note that the foregoing
parameters satisfy the following equality:
.DELTA..times..times..DELTA..times..times..delta..times..times..times.
##EQU00002## According to EQ. (1), a travel .DELTA.X of roughly 1
mm would be sufficient at a relative motion frequency f=20 Hz, for
example. These and other examples determined using EQ. 1, for
various values of the travel-per-pattern .delta.x, relative motion
frequency, and range of travel, are summarized in Table 1.
TABLE-US-00001 TABLE 1 N .DELTA.t (ms) .delta.x (.mu.m) f (Hz)
.DELTA.X (mm) 100 5 1 20 1 100 5 1 2 10 100 5 1 1 20 100 5 10 20 10
100 5 10 2 100 100 5 10 1 200
In some implementations, in addition to activating either the first
linear actuators 252, or the second linear actuators 254, or both,
the driver 250 can strobe the laser 210 by activating/deactivating
the laser in the following manner. For simplicity, strobing will be
explained for the situation when the driver 250 deactivates the
first linear actuators 252 and activates the second linear
actuators 254, so the fan-shaped beam generator 222 is stationary,
and the linear diffuser 232 is in motion, relative the optical axis
201. Here, the driver 250 can activate the laser 210 when a speed
of the linear diffuser 232 exceeds a predetermined speed, and
deactivate the laser when the linear diffuser has a speed smaller
than the predetermined speed. Such slowdown conditions occur when
the linear diffuser 232 changes direction as part of the motion
cycle. Strobing the laser 210 in this manner ensures that a
sufficiently large number of random speckle patterns are averaged
even for very short exposure times.
It was noted above that parameters to be used for optimizing
de-speckling quality of the illumination line 237 are a frequency
of the motion of the diffuser 232 relative the fan-shaped beam
generator 222; and a measure of random differences of (i) the
surface roughness of the (second) linear diffuser 232 at different
locations of the first scan path 231, and/or (ii) the surface
roughness of the first linear diffuser 222 at different points of
the second scan path 221. Another parameter to be used for
optimizing de-speckling quality of the illumination line 237 is a
difference between a divergence angle corresponding to the
fan-shaped beam generator 222 (e.g., a first diffusion angle
corresponding to the first linear diffuser 222) and a second
diffusion angle corresponding to the (second) linear diffuser 232.
For example, the divergence (first diffusion) angle is 5.degree.
and the (second) diffusion angle is 40.degree.. In general, the
difference between the divergence (first diffusion) angle of the
fan-shaped beam generator (first linear diffuser) 222 and the
(second) diffusion angle of the (second) linear diffuser 232 can be
1%, 5%, 10%, 50%, 100%, 500% or 1000%. This is because the main
function of the (second) linear diffuser 232 is to significantly
increase homogeneity of, and reduce speckle from, the light line
127 projected by the fan-shaped beam generator (first linear
diffuser) 222 onto the (second) linear diffuser. Note that it is
the fine structure and pseudo-random nature of the linear diffusers
222, 232 that causes enhanced uniformity and lower speckle
contrast. Yet another parameter to be used for optimizing
de-speckling quality of the illumination line 237 is a spacing d
between the fan-shaped beam generator 222 and linear diffuser 232.
For example, the spacing d between the fan-shaped beam generator
222 and linear diffuser 232 can be 1, 2, 3, 5, 20, 50 or 100 mm.
Note that the spacing d between the fan-shaped beam generator 222
and second linear diffuser 232 is specified to optimize not only
de-speckling quality of the illumination line 237, but also a
volume and/or apparent size of a package for enclosing the
generator 220, for instance.
The arrangement and functionality of the image acquisition device
240 is similar to the arrangement and functionality of the image
acquisition device 140 described above in connection with FIG. 1A.
Here, the image acquisition device 240 is arranged and configured
to image the object 290 as illuminated with the illumination line
237. An optical axis 242 of the image acquisition device 240 is
arranged in the (y,z) plane and forms an acute angle SA with the
optical axis 201 of the laser-based illumination-fan source 202.
The image acquisition device 240 includes an image sensor and an
optical subsystem that forms an image of the illumination line 237
on the image sensor. Note that, because of the way in which the
illumination line 237 has been produced by the source 202, the
image of the illumination line 237 formed, over an exposure time,
is homogenized and speckle-free. The image sensor of the image
acquisition device 240 is configured to convert the image of the
illumination line 237 into information for producing a digital
image of the line-illuminated object 290.
A way to optimize complexity of a laser-based illumination-fan
source (e.g., 102 or 202), e.g., to simplify its components, such
as the illumination-fan generator (e.g., 120 or 220) and the driver
(e.g., 250), is described next.
FIG. 3 shows another example of a laser-based imager 300 that uses
a homogenized illumination line 337 which can be imaged (and/or
observed) as a low-speckle line. The imager 300 includes a
laser-based illumination-fan source 302 and an image acquisition
device 340. In some implementations, the image acquisition device
340 can be either one of the image acquisition devices 140 or 240
described above in connection with FIG. 1A or 2A. The source 302
has an optical axis 301, here (for example) oriented along the
z-axis, and is configured to output, along the optical axis and
parallel to the (x,z) plane, a planar fan of diffused light 335.
The planar fan 335 is projected onto an object 390 and forms the
illumination line 337 at the intersection of the planar fan with
the object.
The source 302 includes a laser 310 and an illumination-fan
generator 320. In some implementations, the laser 310 can be either
one of the lasers 110 or 210 described above in connection with
FIG. 1A or 2A. The laser 310 is arranged to emit laser light as a
collimated laser beam 311 along the optical axis 301. The generator
320 is arranged and configured to receive the collimated laser beam
311 and to produce the planar fan of diffused light 335.
The generator 320 includes a linear diffuser 322 supported by a
cylindrically-shaped rotation stage 324. Here, the
cylindrically-shaped rotation stage 324 has a rotational axis 351
perpendicular to the optical axis 301, and a cross-section parallel
to the (y,z) plane that is shaped like a circle. In the example
shown in FIG. 3, the rotational axis 351 of the rotation stage 324
is parallel to the y-axis. The linear diffuser 322 is attached over
the entire circumference of the side surface of the rotation stage
324 and, hence, forms a cylindrically-shell shaped linear diffuser
with a direction of diffusion that is tangential to the cylindrical
shell.
In the example shown in FIG. 3, during operation of the source 302,
the cylindrically-shell shaped linear diffuser 322 will be rotated
about the y-axis, i.e., the cylindrically-shell shaped linear
diffuser will be rotated in the direction of diffusion. As such,
the rotation stage 324 includes rotation actuators 352 configured
to cause the rotation stage to rotate the cylindrically-shell
shaped linear diffuser 322 in the direction of diffusion. Here, the
source 302 also includes a driver 350 configured to communicate
with the rotation actuators 352. In other implementations, the
driver 350 is external to the source 302 and communicates with the
rotation actuators 352 through a corresponding communication
channel.
In some implementations, the diffusive properties of the
cylindrically-shell shaped linear diffuser 322 can be the same or
similar to the diffusive properties of one of (i) the linear
diffusers 122 and 132 described above in connection with FIG. 1A,
and (ii) the linear diffusers 222 and 232 described above in
connection with FIG. 2A. Also, the cylindrically-shaped rotation
stage 324 is configured to transmit light emitted by the laser 310.
For example, the cylindrically-shaped rotation stage 324 can
include a material, e.g., glass or a plastic, which is transparent
to the laser light. As another example, the cylindrically-shaped
rotation stage 324 can have a slot parallel to the plane (x-z) and
be filled with a medium (e.g., air, glass, plastic, etc.) that can
transmit laser light through the rotation stage.
Referring now to operation of the source 302, the laser 310
projects the laser beam 311 onto an input portion 322A of
cylindrically-shell shaped linear diffuser 322 as a beam spot 313.
Note that the direction of diffusion of the cylindrical-shell
shaped linear diffuser 322 for the input portion 322A is along the
x-axis. For this reason, the input portion 322A transmits light
corresponding to the beam spot 313 to form a fan-shaped beam 323A
parallel to the (x,z) plane. As such, the input portion 322A
projects the fan-shaped beam 323A onto an output (diametrically
opposite) portion 322B of cylindrical-shell shaped linear diffuser
322 as a diffused-light contour 327 along the x-axis. Note that the
direction of diffusion of the cylindrically-shell shaped linear
diffuser 322 for the output portion 322B is also along the x-axis,
because the output portion 322B is diametrically opposite to the
input portion 322A. For this reason, the output portion 322B
transmits light corresponding to the diffused-light contour 327 to
form the planar fan of diffused light 335 parallel to the (x,z)
plane. Note that that planar fan 335 is a superposition of
fan-shaped beams 323B (which are parallel to the (x,z) plane), each
of these fan-shaped beams being formed by the output portion 322B
by diffusing light radiated from a corresponding point of the
diffused-light contour 327. As such, the output portion 322B
projects the planar fan of diffused light 335 onto the object 390
as the illumination line 337.
During operation of the source 302, the driver 350 activates the
rotation actuators 352, which in turn cause the rotation stage 324
to rotate the cylindrical-shell shaped linear diffuser 322 about
the y-axis, such that its input portion 322A and output portion
322B are continuously moving in opposite directions. In this
manner, the stationary (relative to the optical axis 301) beam spot
313 will be formed at multiple points of the moving (relative to
the optical axis 301) input portion 322A, each point with its own
local roughness profile. As such, multiple instances of the unitary
planar fan 323A formed by the moving input portion 322A will be
randomly different from each other, so multiple instances of the
stationary (relative to the optical axis 301) diffused-light
contour 327 formed on the moving (relative to the optical axis 301)
output portion 322B will also be randomly different from each
other. Moreover, each of the multiple instances of the stationary
diffused-light contour 327 will be formed at different locations of
the moving output portion 322B, each location with its own local
roughness profile. As such, multiple instances of the planar fan
335 formed by the moving output portion 322B will be randomly
different from each other, so multiple instances of the stationary
illumination line 337 formed on the stationary object 390 will also
be randomly different from each other. The randomly different
speckle patterns corresponding to the multiple instances of the
stationary illumination line 337 will average out over an exposure
time of the image acquisition device 340, so the stationary
illumination line 337 will be imaged by the image acquisition
device as speckle-free line. Note that in this case, the randomness
of the speckle patterns corresponding to the multiple instances of
the stationary illumination line 337 is caused, at least in part,
by a combination of (i) the random differences of the surface
roughness at the different points of the input portion 322A, and
(ii) the random differences of the surface roughness at the
different locations of the output portion 322B.
To ensure that the illumination line 337 can be imaged as a
low-speckle line, the driver 350 causes the rotation stage 324 to
rotate the cylindrical-shell shaped linear diffuser 322 with a
predetermined rotation frequency. In this manner, the input portion
322A and the output portion of the cylindrical-shell shaped linear
diffuser continuously move relative to each other, along the
x-axis, with a predetermined speed. The predetermined rotation
frequency is proportional to the ratio of the predetermined speed
and the diameter of the cylindrical-shell shaped linear diffuser
322 (i.e., the distance along the z-axis between the input portion
322A and the output portion 322B.) For a diameter in the range of
5-25 mm, the predetermined rotation frequency can be in the range
of 50-500 Hz. A particular value of the diameter of the
cylindrical-shell shaped linear diffuser 322, and the rotation
frequency can be chosen based on a balance of the diffuser material
chosen, the eye safety level required, and the fan angle (of the
planar fan of diffused light 235) desired in the field. For
example, 30.degree. (+/-15.degree.) linear diffusing material can
be wrapped around a 20 mm-diameter rod lens of glass (e.g., N-SF8
material). The input beam 313 to the rod lens-based
illumination-fan generator 320 would be spread roughly +/-5 mm
(corresponding to a 10 mm diffused-light contour 327) by the time
it reached the exit face 322B of the rod. The optical power of the
exit face 322B of the rod "straightens out" the fan-shaped beam
323A, bringing it towards a collimated condition. Then the final
surface passed through is the 30.degree. linear diffusing material
on the exit face 322B, providing, for laser safety purposes, the
extended source condition on the exit face, and homogenizing the
planar fan of diffused light 235. The rotation frequency with which
the cylindrical-shell shaped linear diffuser 322 is to be rotated
to reduce speckle contrast to a predetermined level can be
determine as described above in connection with FIG. 2A.
The arrangement and functionality of the image acquisition device
340 is similar to the arrangement and functionality of the image
acquisition device 140 or 240 described above in connection with
FIG. 1A or 2A. Here, the image acquisition device 340 is arranged
and configured to image the object 390 as illuminated with the
illumination line 337. An optical axis 342 of the image acquisition
device 340 is arranged in the (y,z) plane and forms an acute angle
SA with the optical axis 301 of the laser-based illumination-fan
source 302. The image acquisition device 340 includes an image
sensor and an optical subsystem that forms an image of the
illumination line 337 on the image sensor. Note that, because of
the way in which the illumination line 337 has been produced by the
source 302, the image of the illumination line 337, formed over an
exposure time, is homogenized and speckle-free. The image sensor of
the image acquisition device 340 is configured to convert the image
of the illumination line 337 into information for producing a
digital image of the line-illuminated object 390.
In conclusion, the disclosed technologies use a laser that emits
laser light, a fan-shaped beam generator and one or more linear
diffusers, without or with relative motion between them, for
illuminating an object with a line of the laser light. Here, the
fan-shaped beam generator can itself be a linear diffuser, or
either a Powell lens or a cylindrical lens. The illumination line
produced in accordance with the disclosed technologies is
homogenized and can be imaged (and/or observed) as a low-speckle
line for the following reasons. The angular diversity provided by
the one or more linear diffusers homogenizes the laser light along
their common diffusion direction to avoid diffractive defects and
reduce sparkle on objects illuminated with the homogenized
illumination line. The relative motion of the linear diffusers
causes changes of a speckle pattern of the illumination line during
an exposure time without affecting the width of the illumination
line along a transverse direction (perpendicular to the diffusion
direction). Moreover, the spatial profile of the illumination line
along the transverse direction remains the Gaussian profile of the
emitted laser light. In this manner, the illumination line, at any
slice taken along the propagation direction, which is perpendicular
to the diffusion direction and the transverse direction, will have
the original Gaussian profile along the transverse direction, and,
in the diffusion direction will be homogenized, and will have a
predictable line length controlled by the diffusion angles of the
two or more linear diffusers.
A few embodiments have been described in detail above, and various
modifications are possible. The disclosed subject matter, including
the functional operations described in this specification, can be
implemented in electronic circuitry, computer hardware, firmware,
or in combinations of them, such as the structural means disclosed
in this specification and structural equivalents thereof.
For example, a driver (e.g., 150, 250, 350) can include at least
data processing apparatus and medium. The data processing apparatus
can be one or more hardware processors, e.g., central processing
units (CPUs), graphic processing units (GPUs), or combinations
thereof, which can each include multiple processor cores. The
medium is computer-readable medium that can include both volatile
and non-volatile memory, such as Random Access Memory (RAM) and
Flash RAM, for instance. The medium encodes instructions, that when
executed by the data processing apparatus, cause the driver to
implement aspects of processes disclosed herein, for instance. The
connector(s) (shown in dashed line in FIGS. 1A, 2A and 3) can be
one or more of USB connectors, Ethernet connectors, or other
network connectors. In general, the connector(s) can represent any
data communication link(s) and power transfer link(s), or
combination thereof, implemented via physical cables or
wirelessly.
While this specification contains many specifics, these should not
be construed as limitations on the scope of what may be claimed,
but rather as descriptions of features that may be specific to
particular embodiments. Certain features that are described in this
specification in the context of separate embodiments can also be
implemented in combination in a single embodiment. Conversely,
various features that are described in the context of a single
embodiment can also be implemented in multiple embodiments
separately or in any suitable subcombination. Moreover, although
features may be described above as acting in certain combinations
and even initially claimed as such, one or more features from a
claimed combination can in some cases be excised from the
combination, and the claimed combination may be directed to a
subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a
particular order, this should not be understood as requiring that
such operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed,
to achieve desirable results. In certain circumstances,
multitasking and parallel processing may be advantageous. Moreover,
the separation of various system components in the embodiments
described above should not be understood as requiring such
separation in all embodiments.
Other embodiments fall within the scope of the following
claims.
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